1. Field of the Invention
This invention relates to a bearing device and a motor mounted with the bearing device, particularly, relates to a technology suitably applied for a bearing device that is mounted on a motor to be installed in disc drive equipment, which drives a recording medium in disciform such as a hard disc and an optical disc to rotate.
2. Description of the Related Art
It has been commonly required for conventional motors to be smaller in dimensions. Particularly, it has been strongly required that a motor to be installed in disc drive equipment, which drives a recording medium in disciform such as a hard disc and an optical disc to rotate, was not only smaller in dimensions but also thinner in thickness.
One example of such a conventional motor is disclosed in the Japanese publication of unexamined patent applications No. 2003-120662.
According to the Japanese publication of unexamined patent applications No. 2003-120662, the motor is provided with the inner sleeve member 48, which supports the shaft part 50 as a slide bearing, and the outer sleeve member 46, wherein the inner sleeve member 48 is fixed on an inner peripheral surface of the outer sleeve member 46. Both the inner and outer sleeve members are fixed integrally by fixing adhesive.
More specifically, the inner sleeve member 48 is provided with the groove 112 for fixing adhesive on an outer peripheral surface in the axial direction. Fixing adhesive is filled in the groove 112, and then the inner sleeve member 48 is fixed to the outer sleeve member 46.
Further, according to another prior art, another motor is also known. The motor is provided with a sleeve, which supports a shaft as a slide bearing, and a housing, wherein the sleeve is fixed on an inner peripheral surface of the housing.
Furthermore, in the motor, a circumferential groove is provided on an inner peripheral surface of the housing or on an outer peripheral surface of the sleeve.
More, fixing adhesive is filled in the circumferential groove, and then the sleeve and the housing are fixed integrally.
In reference to FIGS. 10a-12, a motor provided with a sleeve and a housing either one of which is provided with a circumferential groove is briefly described next.
FIG. 10a is a side elevation view of a first sleeve having no circumferential groove on an outer peripheral surface of the first sleeve according to a first prior art.
FIG. 10b is a cross sectional view of a first housing having a circumferential groove on an inner peripheral surface of the first housing according to the first prior art.
FIG. 11a is a side elevation view of a second sleeve having a circumferential groove on an outer peripheral surface of the second sleeve according to a second prior art.
FIG. 11b is a cross sectional view of a second housing having a circumferential groove on an inner peripheral surface of the second housing according to the second prior art.
FIG. 12 is a cross sectional view of the second sleeve and housing shown in FIGS. 11a and 11b, which are fixed integrally by fixing adhesive.
In FIG. 10a, a first sleeve 105A is provided with an outer peripheral surface 105Aa and no groove to be formed on the outer peripheral surface 105Aa.
In FIG. 10b, a circumferential groove 102A is formed on an inner peripheral surface 104Aa of a first housing 104A.
The first sleeve 105A shown in FIG. 10a is inserted into the first housing 104A so as to confront the outer peripheral surface 105Aa of the first sleeve 105A with the inner peripheral surface 104Aa of the first housing 104A. The first sleeve 105A is fixed to the first housing 104A by means of not shown fixing adhesive filled in the circumferential groove 102A.
On the other hand, in FIG. 11a, two circumferential grooves 103B1 and 103B2 (hereinafter generically referred to as “circumferential groove 103B”) are formed on an outer peripheral surface 105Ba of a second sleeve 105B while the two circumferential grooves 103B1 and 103B2 are disposed so as to be apart from each other in an axial direction. In FIG. 11b, two circumferential grooves 102B1 and 102B2 (hereinafter generically referred to as “circumferential groove 102B”) are formed on an inner peripheral surface 104Ba of a second housing 104B while the two circumferential grooves 102B1 and 102B2 are disposed so as to be apart from each other in the axial direction.
Further, the second sleeve 105B is inserted into the second housing 104B so as to confront the outer peripheral surface 105Ba of the second sleeve 105B with the inner peripheral surface 104Ba of the second housing 104B. The second sleeve 105B is fixed to the second housing 104B by means of not shown fixing adhesive filled in the circumferential grooves 102B and 103B.
As shown in FIG. 12, the circumferential groove 103B of the second sleeve 105B confronts with the circumferential groove 102B of the second housing 104B and room 106 is formed across the second sleeve 105B and the second housing 104B when the second sleeve 105B is inserted into the second housing 104B. Fixing adhesive 107 is filled in the room 106. Filling the fixing adhesive 107 in the room 106 makes adhesive strength between the second sleeve 105B and the second housing 104B improve more while the adhesive strength is coupled with shearing strength of the fixing adhesive 107.
In the meantime, a number of major component parts constituting a bearing of a conventional motor has been four, that is, a sleeve, a shaft, a flange and a hub, wherein the flange will be described as a thrust ring. However, a motor having a complicated structure has been developed recently so as to obtain sufficient dynamic characteristics of a motor even though the motor has been minimized in dimensions and thinned in thickness.
More specifically, many conventional motors mounted with a bearing that is constituted by five component parts have been proposed. In such a bearing, the housing for fixing the sleeve mentioned in the prior arts has been added in addition to the four major component parts mentioned above.
On the contrary, a natural vibration frequency of a motor fluctuates as a number of component parts of a bearing increases. By the fluctuation of vibration frequencies, a ratio of motors of which resonance frequency is relatively low has been increased in mass production.
In case the resonance frequency of a motor decreases, it possibly occurs that the decreased resonance frequency interferes with a driving frequency of a disc and results in generating extraordinary vibration and noise.
On the other hand, in case disc drive equipment is a hard disc drive to be installed in portable equipment such as a mobile computer, it is required for such a hard disc drive to be able to endure 1000 G of acceleration as a dropping impact-resistant characteristic. In this regard, each member constituting a bearing must be fixed to each other in higher strength.
On the contrary, in the structure of the motor disclosed in the Japanese publication of unexamined patent applications No. 2003-120662, a ratio of adhesion area in the circumferential direction is relatively narrow, and resulting in hardly obtaining sufficient adhesive strength, wherein the inner sleeve member 48 is fixed to the outer sleeve member 46 (rotor hub 8) by filling fixing adhesive in the groove 112.
Further, in the case of a fixing method according to the first prior art shown in FIGS. 10a and 10b in which the first sleeve 105A is fixed to the first housing 104A by filling the fixing adhesive in the circumferential groove 102A, width in the axial direction of the circumferential groove 102A in which the fixing adhesive contacts with the outer peripheral surface 105Aa of the first sleeve 105A is extremely narrow. Consequently, sufficient adhesive strength is hardly obtained.
In this connection, it has been considered that width of a groove was widened or a number of grooves was increased so as to improve adhesive strength. However, there is a limit to improve adhesive strength. Because engaging length of the first sleeve 105A with the first housing 104A in the axial direction was short due to essential designing concept of thinning the total thickness of a motor.
On the other hand, in the case of another fixing method of the second sleeve 105B to the second housing 104B according to the second prior art shown in FIG. 12, the circumferential grooves 102B and 103B are formed on the inner peripheral surface 104Ba of the second housing 104B and on the outer peripheral surface 105Ba of the second sleeve 105B respectively, and the fixing adhesive 107 is filled in both the circumferential grooves 102B and 103B. As a result, filling the fixing adhesive 107 in the room 106 makes adhesive strength improve in consideration of the shearing strength of the adhesive 107.
However, filling the fixing adhesive 107 in the room 106 is extremely difficult in manufacturing.
More specifically, in case an enough amount of fixing adhesive 107 is filled in the circumferential groove 102B of the second housing 104B so as to fill the room 106 sufficiently and to rise above the inner peripheral surface 104Ba, for instance, the risen amount of the fixing adhesive 107 is shaved off by the outer edge of the second sleeve 105B when the second sleeve 105B is inserted into the second housing 104B.
As a result, a void is generated in the room 106.
Further, even in case the fixing adhesive 107 is filled in both the circumferential grooves 102B and 103B, each of the inner edge of the second housing 104B and the outer edge of the second sleeve 105B shaves off respective fixing adhesive 107 filled in the circumferential grooves 102B and 103B from each other. In this regard, there is a further worry that the shaved-off fixing adhesive 107 attaches to other portions or regions other than the room 106.
Furthermore, in case the fixing adhesive 107 is filled in both the circumferential grooves 102B and 103B, the fixing adhesive 107 must be applied on the second housing 104B and the second sleeve 105B almost simultaneously in consideration of a hardening characteristic of the adhesive 107. Consequently, assembling work of the second housing 104B and the second sleeve 105B becomes harder furthermore.
More, providing the room 106 makes wall thickness of the section of the second housing 104B and the second sleeve 105B remarkably thinner, and resulting in generating further problem such that deflective rigidity as a bearing is deteriorated.
As mentioned above, by the respective fixing methods of the sleeve and the housing according to the prior arts in which fixing adhesive is filled in circumferential grooves that extend in the axial direction or the circumferential direction, it is difficult to improve deflective rigidity in the axial direction or the circumferential direction.
Accordingly, a technology that solves the above-mentioned problems and improves deflective rigidity furthermore has been desired.